THE EFFICACY OF CT SCANS FOR IMAGING FOSSILS IN ASPHALTIC PALEONTOLOGICAL DEPOSITS FROM RANCHO LA BREA

Paleontological sedimentary deposits from Rancho La Brea contain geological, osteological, and botanical clasts consolidated by asphalt. The fossilized material in these specimens is best studied after preparation, wherein sediment is removed by a degreasing solvent. However, this manner of preparation entails the loss of data relevant to the geology and paleoecology of the site, including the taphonomy of any non-geological material. To preserve this information, we performed a 45-micrometer CT scan using a Bruker Skyscan 1273 on an asphaltic specimen containing a rare articulated mammalian spine. The density difference between the materials was sufficient to distinguish different types of clasts in the resulting 3D model: bone showed as light gray to white, botanical material presented as dark gray, and sediment showed as white to medium gray. Osteological and geological clasts were distinguished by shape when the color was insufficient. It was also possible to observe differences in grain size based on the varying shade of the finer-grained sediments that are interpreted as a single solid in imaging, although detailed geological analysis may require a higher resolution CT scan. This study demonstrates that CT scanning can preserve a copy of the geological context when osteological material must be prepared for paleontological collection, though the value of this method must be balanced against limiting factors such as cost and size, based on available equipment.